Near field communication (NFC) is an emerging radio frequency identifier (RFID) based technology that promises to enable wireless transfer of data over very short distances and replace regular contact based interactions with a contactless interaction between two devices or a device and a card placed in close proximity. Typical usages include coupons, identifier (ID) cards, mobile payments, and peer to peer connections between devices.
Various applications may be enabled by NFC technology including many that compute continuum and mobile payment. For example, the Windows™ 8 Operating System offers support for proximity usages, where users with NFC devices may “tap and share” and/or “tap and pair” by bringing NFC enabled devices in proximity with one another. Another emerging application along with security services is “tap and pay,” where mobile platforms (e.g., Ultrabooks, tablets and smartphones) may be used as a personal point of sale (POS) terminal to read NFC enabled credit cards/smartphones for payment applications.
The payment and proximity usages of the NFC have dramatically different reader performance requirements on the integrated NFC device. For example, EMVco (Europay, MasterCard and Visa) which governs payment terminals, may require more RF power (approximately 5 to 6 times than normal operational power) from the integrated reader to support NFC communication with NFC enabled credit cards. In contrast, proximity usage which is certified by the NFC Forum does not require the reader to emit a very strong RF field, such that a less complicated NFC solution may be used.
Currently, there are multiple low cost, small size and relatively simple to integrate NFC solutions that may support proximity usage. A challenge that designers face in the existing NFC solutions is to meet, for example, the performance and user experience requirements of the EMVco with minimum added cost, limiting size increases, and minimal additional power consumption.
NFC systems may rely on the near field coupling of a magnetic field between two coils tuned near resonance.
As shown by the following equation:Pr∝Pt·Q·k
The power received by the NFC card being read (Pr) is determined by the transmit power (Pt), quality factor of the two coils (Q), and the coupling coefficient between them (k). The quality factor (Q) is more or less fixed per the NFC radio design, while the coupling coefficient is mainly determined by how much magnetic flux generated by the transmit (Tx) coil is able to penetrate the receive (Rx) coil and induce electrical current. Therefore there is a dependency on the size of the coils and ferrite material quality.
Conventionally, a larger coil with larger and high quality ferrite can be used to increase the coupling factor (k) which in turn increases the power received by the NFC card. However, as mobile devices get smaller and more compact, it becomes more challenging to allocate a relatively large space for antennas. Furthermore, device manufacturers may face the need for larger and more expensive ferrite material. Increasing the transmit power (Pt) may require new NFC chip designs and may significantly increase system power consumption.